题解

建议降红

#include <bits/stdc++.h>
#define ll long long
#define endl '\n'
#define pii pair<int, int>
using namespace std;
const int maxn = 1e6 + 5;
int n;
string s;
int main() {
    cin >> s;
    n = s.size();
    s = ' ' + s;
    int ans = 0;
    for (int i = 4; i <= n; i++) {
        if (s[i] == 'N' && s[i - 1] == 'O' && s[i - 2] == 'O' && s[i - 3] == 'N') {
            ans ++;
        }
    }
    cout << ans << endl; 
}